"Lights-out" CNC means running the shop unattended — usually overnight — with bar feeders, pallet changers, and probing handling everything until a human walks back in. Done right, it doubles capacity for free. Done wrong, it's a broken spindle waiting to happen. Here's when to use it.

The math nobody puts on a slide

A typical CNC machine running 8 hours a day, 5 days a week is utilized about 2,000 hours/year. Push it to lights-out and you can hit 5,000–6,000 hours. On a $200,000 machine, the depreciation per hour drops from $40 to $13. That's the entire reason shops with bar feeders and tower magazines beat shops without them on long-run jobs.

When lights-out makes sense

Long-running production parts (60+ minute cycles, hundreds of pieces)
Bar-fed lathe work in 1"–4" stock
Pallet-changed milling on consistent fixturing
Wire EDM (built for unattended running)
5-axis cycles on aerospace structural parts where one fixture loads multiple ops

When it burns cash

Prototype runs (single setup, no time amortized)
Tight-tolerance work that needs in-process measurement and adjustment
Short cycles where chip evacuation and tool wear vary too fast for probing
Tough-to-machine alloys (Inconel, Ti-6Al-4V) where tool monitoring matters more than throughput
Any job where a crash means scrapping a $5k workholding fixture

What you need on the machine to run lights-out safely

In-process probing (Renishaw / Heidenhain) for offset compensation
Tool breakage detection (laser or touch probe)
Chip conveyor + high-pressure coolant
Bar feeder or pallet changer for parts feed
Macros that abort cleanly on alarm and flag the next part
Camera + offsite alerting on door open / alarm fault

What you need around the machine

Fire suppression rated for your coolant (oil mist + chip pile is a known hazard)
Insurance carrier informed and policy worded for lights-out
Local FD aware of the building
Backup generator or graceful-shutdown UPS so a power blip doesn't scrap the whole stack

How we use lights-out at Emory

We run our bar-fed lathes overnight on long-cycle stainless and aluminum parts. Our wire EDMs run around the clock once a profile is dialed in. Our 5-axis cells are pallet-changed, with operator-staged fixtures so the morning shift can re-tool while the spindles keep running. We don't run mills lights-out on new prototypes or new alloys until we have probing data on tool wear.

The conversation to have with your supplier

On a high-volume reorder, ask: "Will you be running my part lights-out, and if so, what's your probing and abort plan?" A real shop will explain it in 30 seconds. A shop that says "we always have someone watching" on a 200-piece overnight run is either lying or losing money on your job.

If you have a long-running production part and want it priced as a lights-out run with the savings passed back to you, send us your drawing. We'll show the math both ways.